using System;

using Org.BouncyCastle.Crypto;
using Org.BouncyCastle.Security;

namespace Org.BouncyCastle.Crypto.Paddings
{
	/**
	* A padder that adds Pkcs7/Pkcs5 padding to a block.
	*/
	public class Pkcs7Padding
		: IBlockCipherPadding
	{
		/**
		* Initialise the padder.
		*
		* @param random - a SecureRandom if available.
		*/
		public void Init(
			SecureRandom random)
		{
			// nothing to do.
		}

		/**
		* Return the name of the algorithm the cipher implements.
		*
		* @return the name of the algorithm the cipher implements.
		*/
		public string PaddingName
		{
			get { return "PKCS7"; }
		}

		/**
		* add the pad bytes to the passed in block, returning the
		* number of bytes added.
		*/
		public int AddPadding(
			byte[]  input,
			int     inOff)
		{
			byte code = (byte)(input.Length - inOff);

			while (inOff < input.Length)
			{
				input[inOff] = code;
				inOff++;
			}

			return code;
		}

		/**
		* return the number of pad bytes present in the block.
		*/
		public int PadCount(
			byte[] input)
		{
			int count = (int) input[input.Length - 1];

			if (count < 1 || count > input.Length)
			{
				throw new InvalidCipherTextException("pad block corrupted");
			}

			for (int i = 1; i <= count; i++)
			{
				if (input[input.Length - i] != count)
				{
					throw new InvalidCipherTextException("pad block corrupted");
				}
			}

			return count;
		}
	}

}
